The invention relates an air damper for movable elements, in particular in automobiles, comprising a hollow cylinder which is open at one end thereof and a piston which is slidably guided within the cylinder in a longitudinal direction thereof.
It is known, for example, to damp the covers of gloveboxes by means of suitable damping elements. The unlocked cover, by virtue of its own weight,automatically pivots to the opened position with the opening motion being attenuated by a damper. In this conjunction, rotary dampers have become known in which a rotor is rotatably disposed in a casing with the rotor, in a cavity of the casing, being immersed into a viscous medium such as silicone oil or silicone grease, and rotating therein. The rotation-damping element has a pinion which interacts with a toothed rack. Thus, displacing the toothed rack will result in a rotation of the rotation damper or rotor which is attenuated accordingly.
The utility model DE 295 18 171 has made known a damping element including a piston which is slidably guided in a longitudinal direction thereof. The piston separates the cylinder into two regions which are interconnected by a groove extending in the longitudinal direction of the cylinder in the piston. The cross-section of flow from one cylinder space to the other may be chosen differently so that a choking of the flow of air and, hence, an attenuation of the piston motion is achieved in this way. A drawback of the air dampers which have become known are the differing damping performance caused by tolerances.
It is the object of the invention to provide an air damper which is comprised of few components and has reproducible attenuation characteristics.
According to the invention, the object is attained by the features of claim 1.
The separation means fixed to the piston and the cylinder inside wall separates the hollow space of the cylinder into a first and a second portion which are arranged adjacent to each other in the longitudinal direction. These portions define two cylinder spaces the volumes of which depend on the position of the piston in the cylinder. The length of the element connecting the points of fixation is adjustable. The first one of the portions is in communication with the atmosphere so that if its volume changes it will exchange its air with the atmosphere. The second portion defined by the separation means is arranged adjacent to the bottom of the cylinder. The second portion has at least one opening for the flow of air wherein the opening may be provided in the cylinder and/or the piston. For an attenuation. the piston is guided within the hollow space of the cylinder in the longitudinal direction of the cylinder with the air exiting in a choked state through the opening from the second portion, which leads to an attenuation of the piston motion. Likewise, air which flows in and is delayed by the opening, attenuates the motion of the piston if the volume of the second portion is increased.
In a preferred aspect of the invention, the opening in the second portion is provided at the bottom of the cylinder. In this arrangement of the opening, air will exit from and enter the cylinder in a longitudinal direction. Consequently, it is possible for the air to enter and exit throughout the lifting operation of the piston.
It is advantageous to fit the opening with at least one inlet valve for passing a predetermined flow of admission air therethrough. The valve enables a flow of air to enter the second portion so that if the volume of the second portion increases the speed of motion may be controlled by means of the flow opening of the inlet valve.
Advantageously, the inlet valve is provided as a check valve which blocks a flow out of the cylinder and in which a valve body is biased by a spring means towards the inlet direction. The effect of the biased valve body is that a flow of air will commence only following a certain increase in volume.
The inventive air damper advantageously has at least one bore for passing a predetermined flow of entering and exiting air therethrough. Such a calibrated bore determines the damping characteristics for either direction of piston displacement. If the inlet valve is additionally provided also in the second portion its effect will add to the effect of the calibrated bore if the piston is extracted.
Expediently, the separation means is formed from an elastomer. The separation means thus formed may adapt to the piston position if the piston undergoes a displacement. Also, such a separation means is easy to manufacture and is of a tightness sufficient to separate the first and second portions from each other.
In an advantageous aspect of the invention, the separation means is designed as a bellows which is extendable in the longitudinal direction. The bellows is extended when the piston is in a completely retracted position and is contracted when the piston is in a respective extracted position. The bellows may be dimensioned in its length such that it exerts a restoring spring force when in its extended position, i.e. when the limit of the stroke of the piston is reached.
In another aspect of the inventive air damper which is advantageous as well the separation means is designed as a rolling diaphragm. The rolling diaphragm will adapt as well to the position of the piston within the cylinder so that a separation of the portions within the hollow space of the cylinder will be effected only in a flexible manner.
The separation means preferably is in communication with the hollow space of the cylinder at the open end thereof. The communication of the separation means with the hollow space of the cylinder at the open end thereof causes the change in volume to be as large as possible if the piston is displaced in order to achieve sufficient attenuation.
For a fixation of the separation means, one end of the separation means is clamped between an end surface of the cylinder and a cover plate on the cylinder end surface. The separation means is held here on the cylinder end surface.
For a fixation of the separation means, the end-surface border of the cylinder has a circumferential groove which is engaged by a circumferential rib of the separation means. In this type of a location device, the separation means has disposed its rib in the groove on the end surface of the cylinder and the cover plate is clamped on the cylinder, which clamps the separation means.
The outer diameter of the piston is smaller than the inner diameter of the cylinder so that a precise-fit manufacture of the piston or a seal between the piston and the cylinder wall is not required.
Advantageously, the piston and the piston rod comprise an axial bore into which a rod is inserted which centrally extends into the hollow space of the cylinder. The piston may be guided here on the rod. The rod imparts large stability to the damper against cross forces applied to the piston rod.
In a particularly preferred aspect, the piston comprises two sections with one end of the separation means being clamped between the sections. Apart from the piston rod. the sections may serve as a guide for the piston as well. Expediently, the piston is guided through the section facing away from the separation means.
For a connection of the separation means to the piston, one of the sections comprises a circumferential groove which is open in an axial direction and is engaged by a circumferential rib of the separation means. The sections of the pistons may be interconnected by being welded together and/or being joined by an adhesive, which depends on the material chosen. Preferably, the cylinder and the piston are formed from a plastic material.